The present invention relates to double action stamping presses and, more particularly, to a method and apparatus for balancing a double action stamping press.
Double action presses comprise an inner and outer slide both of which are driven off a single crankshaft wherein two stamping operations are performed in one stroke. Often, a press of this type is used in the container industry as a press in the manufacture of beverage container cups or shells. Strip stock material is fed into the double action shell or cupping press wherein the outer slide blanks out a disc, and then the inner slide die almost immediately forms the disc into a shallow cup.
During this type of operation, the double action press has typically been run at approximately 150 stokes per minute (spm). However, due to today's current output demand, double action presses are being run at approximately 350 spm more than double the past rate. At these higher stroke speeds, inertia forces generated by the vertically reciprocating inner and outer slides and upper dies create strong vibrations in the press structure which are transmitted into the press foundation and surrounding building structure.
Thus, by increasing twofold the number of strokes per minute, severe vibrations are produced which quickly cause damage to the press structure, press foundation, and the surrounding building structure. Therefore it is necessary to minimize the vibrations created by the inertia forces of the slides and upper dies attached to slides by balancing the press. It is generally difficult to balance a double action press because of the phase difference between the inner and outer slides and also the difference in stroke lengths.
A prior art solution isolates the press structure from the building structure such that the manifested vibrational forces are not transmitted or reflected thereto. This is accomplished by providing a separate, dedicated concrete foundation of several hundred thousand pounds isolated from the building structure on which the double action press must be mounted. This solution however does not reduce vibrations created by the inertia forces, and although the building structure is relatively free from damaging vibration, the press structure and foundation are not.
Another type of balancer is the counter rotating geared shafts with counter weights. The inertia forces of the slides are then balanced by the counterweighted rotating shaft. However, this rotating inertia is stopped and started as the press slides go up and down, and takes five or six strokes to fully stop the press for maintenance, die change, or the like.